Lithium, AGM, mixed battery chemistry and solar.

[Samro]

I am planning the electrics for my new vehicle (when it arrives soon) and I have a question about charging.

I will have:
150W of solar
30A DC-DC charger.
110Ah LifePo leisure battery.

My question relates to the DC-DC and the connection of the solar controller:

Whilst I initially wanted to use a Victron Smart MPPT, I have purchased a Voltronic Duo 250 (MPPT) as I wanted the solar to provide a trickle to the engine start battery as well as charge the LifePo leisure battery.

BUT - If I discard the idea of using the Voltronic unit and use a Victron controller to provide all solar output to the starter battery, will the DC-DC charger distribute excess charge to the leisure bank and as a result charge my leisure battery satisfactorily?

Is this a bad idea because of the potential inefficiencies?

 

[yossarian]

Some additional info, hope it helps:

Your 30A DC to DC converter is equivalent to around 400W.

The lifepo4 battery is far more efficient than a lead acid at accepting charge.

Observations:

The DC DC charger can outpace the mppt so some way to prevent this from happening (and running down your battery) is essential if you connect mppt -> agm -> lifepo4.

Efficiency would be improved if you charged mppt -> lifepo4 -> agm.

Regards

Edits: a -> A

 

[Samro]

Thanks @yossarian. You’ve confirmed my initial thoughts and I will stick with the voltronic controller.

 

[t0mb0]

You want to connect both your DD-DC and MPPT in the traditional way to charge your leisure battery, anything else is going to have very strange results.

However, read the votronic instructions carefully, I’m not sure you can use the built-in trickle charge functionality for the starter if you have a lithium leisure battery because of the voltage mismatch between the two. If this is the case, you need a more sophisticated way of achieving the trickle charge, I think ablemail sell a unit that might do the trick.

 

[Samro]

You want to connect both your DD-DC and MPPT in the traditional way to charge your leisure battery, anything else is going to have very strange results.

However, read the votronic instructions carefully, I’m not sure you can use the built-in trickle charge functionality for the starter if you have a lithium leisure battery because of the voltage mismatch between the two. If this is the case, you need a more sophisticated way of achieving the trickle charge, I think ablemail sell a unit that might do the trick.

It seems from the manual that the Voltronic Duo 250 that the 1A trickle output mode is fixed to “Lead”, whereas the main (Max 15A) output to the leisure bank can be set (with the use of the jumpers) to LifePo mode. I am confident that it will operate within the correct parameters so long as I install the temp sensor, but not happy about how little info the unit will provide without the use of third party solution such as https://amzn.to/2Qk6IBk

I’m happy to use the Voltronic, but not too keen on the lack of monitoring. (No data will be recorded and I’ve gotten used to the convenience of Victron Connect!)

I am surprised at the lack of available products that will do what I want!

 

[Dellmassive]

have a look at some other option for "reverse charging" the starter battery. . . .

[Guide] Battery Maintainer (for Starter battery) -- How I Done It --

[Guide] Battery Maintainer (for Starter battery) -- How I Done It -- Right so its that time of year again . . . . . . . . Winter & (Lockdown 2020) The van might be layed up not being used, which will lead to a flat battery in around 3 weeks. The cold weather doesn't help the battery's...

www.t6forum.com

.

 

[yossarian]

I am surprised at the lack of available products that will do what I want!

Indeed. Given that smps are pretty much a commodity now. Roll your own is starting to look attractive which is, quite frankly, crazy.

 

[t0mb0]

If you want shiny bar graphs of solar activity, go for victron and add a separate trickle charger gizmo for the starter battery. Otherwise, just wire in the votronic you already have I suppose. I guess the monitoring/plotting side of solar is neat to have, but having got over the initial entertainment, it doesn't seem like particularly critical functionality. I assume your battery already gives you state of charge in some form if you're wondering about more levels of monitoring?

 

[VanDamMan]

Just been looking on an Australian web site at REDARC Battery to battery Solar etc….might be of interest

Portable power tech

REDARC BCDC1225D DC Battery to Battery Charger 25A (Dual input)​

• Battery Chargers
• Battery to Battery Chargers
• REDARC BCDC1225D DC Battery to Battery Charger 25A (Dual input)

Item Code : 8058 / Manufacturer : REDARC

REDARC BCDC1225D 25A 12V DC Battery to Battery charger - charge your aux battery on the move from both solar and alternator​

£373.49 (inc. vat)​

In stock.
+-



Exclusive to Portable Power Technology in the UK, the REDARC range of battery to battery chargers are designed and tested in Australia for the toughest conditions to provide easy and efficient in-vehicle charging of batteries.
The new REDARC BCDC1225D is a 12V/24V input 25A output In-vehicle Battery to Battery charger. Incorporating dual input technology the BCDC1225D will easily and efficiently charge your 12V auxiliary battery on the move from alternator and solar utilising the integrated MPPT controller.
The new "Dual" version of the highly acclaimed Redarc BCDC range of battery to battery chargers provides simultaneous charging of your auxiliary battery from DC and solar with a suitable PV panel connected. Green power priority ensures that power generated from solar is used first before supplementing any short fall from the vehicle alternator.
Three models at 25A ,40A and the new 50A now replace the previous BCDC varients making selection of the correct charger incredibly simple. The BCDC Dual can be used with both 12V and 24V conventional AND smart alternators (EU5/EU6) and is capable to efficiently and safely charge all common lead acid battery chemistries (AGM/Sealed lead acid/Calcium). The unit also now has a lithium (LiFePO4) charging profile to reliably fast charge a 12V lithium auxiliary battery.
The BCDC battery to battery charger range features a Maximum Power Point Tracking (MPPT) solar regulator, extracting the maximum amount of power from 12V solar panels to charge the auxiliary battery, even during low light conditions, when you’re parked.
Proven and Tested
Compact in size, easy to install and fully sealed - water, dust and vibration are no match for the in-vehicle battery to battery charger.
Designed to handle the roughest tracks in outback Australia and adopted by all the major UK commercial vehicle converters, the BCDC won’t let you down and is suitable for installation in harsh environments or marine applications.

• Features
• Specifications
  Input Voltage Range : 9V-32V
  Maximum Charging Voltage (Absorption) : 14.6V/15.0V/15.4V
  Output Current : 25A
  Integrated MPPT solar regulator : Yes
  Solar Switch on voltage : 17.5V
  Working Temperature Range : -15 to + 80 deg c
  Dimensions : 165 x 120 x 37mm
  Weight : 850g
  Warranty : 2 years
  • REDARC BCDC Dual Brochure
  • REDARC BCDC Dual E mark Certificate

 

[Samro]

have a look at some other option for "reverse charging" the starter battery. . . .

[Guide] Battery Maintainer (for Starter battery) -- How I Done It --

[Guide] Battery Maintainer (for Starter battery) -- How I Done It -- Right so its that time of year again . . . . . . . . Winter & (Lockdown 2020) The van might be layed up not being used, which will lead to a flat battery in around 3 weeks. The cold weather doesn't help the battery's...

www.t6forum.com

Thanks for this @Dellmassive

The below info was what I was thinking of doing, but I can’t decide if it is an efficient thing to do.

4# What about DC-DC and Separate solar? . . . . . . . .

This is an interesting one. . . . . Most people have a DC-DC that charges the AUX battery when the engine is running . . .

and a solar system connected to the AUX battery for when static or in fact at any other time there is enough solar about. . . .

in this configuration, with the van static for a long time the start will run flat . . . but there is any easy fix.

If the Solar was re-connected to the starter battery (instead of the AUX battery)

And there was enough solar to generate a charge . . . . . . . that starter battery will be charged, then at some point when the starter battery voltage was high enough, The DC-DC charger would kick in and start to charge the AUX . . . . . NET effect is that the one solar setup can charge both battery's (Solar power dependent and yes the DC-DC will cycle on/off as the starter battery voltage rises & falls.

i called it "reverse charge" or "auto VSR"

I think I’ll stick to my original plan and forfeit the Victron “gloss” as per the comment by @t0mb0.

 

[AussieMick]

The Redarc BCDC 1225 d as posted by @VanDamMan is the one I fitted to my van. It has been great . First I had an agm leisure battery fitted and now have a lifepo4 and you can program for either.
It can use up to 25 amps of solar input and is available in models for 40a or 50a.
I have found 25a sufficient so far.
It is an mppt controller and is also suitable for our altenators.
Redarc products are known to be very robust and are a good company to deal with.
My redarc solar blanket stopped working when over 6 months outside of warranty and I rang them and after testing it they replaced it with a new one even though they could have got out of it.
A good product in my opinion.

 

[Samro]

I agree that the Redarc looks to be the quality option, but having already purchased the Voltronic Duo (when I already had a Victron DC-DC), I think I will be fine.

If I’m honest, I’m a sucker for blue boxes and full integration of Victron kit. (It’s just annoying that there is no integrated solution through Victron to do what I want.)

After viewing a lot of threads on this forum referring to various blue boxes, I know I’m not alone in my desire (& weird & sad geekiness) to display all battery/charging data in a manufacturers single app. Plus having the ability to remotely access settings via VRM is something that I really wanted to do... However, on occasion I need to have a word with myself!

Q: Why do I need to complicate a problem after I already did my research and bought the Voltronic Duo?

A: I don’t, but if someone on here came up with an overcomplicated solution to my problem I’d be all ears!..... More to the point... I asked!..... What is wrong with me?